1. Field of the Invention
The present invention relates to a method of manufacturing a metal paste for an internal electrode of a multilayer ceramic capacitor (MLCC), and more particularly, to a method of manufacturing a metal paste for an internal electrode of an MLCC that may manufacture an internal electrode as a thin layer using nano glass added with a rare-earth element and ceramic inhibitor powder of which average particle size is controlled.
2. Description of the Related Art
Currently, ultra high capacitance is required for a multilayer ceramic capacitor (MLCC). The MLCC may achieve the ultra high capacitance by manufacturing each of a dielectric sheet and an internal electrode as a thin film and thereby increasing the number of layers. A method of constructing the MLCC to have the ultra high capacitance may include a method of increasing the number of layers by forming a thickness of the dielectric sheet or the internal electrode as a thin film. In the case of forming the internal electrode as the thin film, shrinkage becomes serious whereby disconnection or aggregation of the internal electrode occurs. Accordingly, defect such as degradation in capacitance, short between internal electrodes, and the like may increase.
The disconnection or aggregation of the internal electrode occurs due to a shrinkage difference since a great sintering difference occurs by using different heterogeneous materials, that is, a ceramic material and a metal material for the dielectric sheet and the internal electrode when manufacturing the MLCC. A method of decreasing the shrinkage of the dielectric sheet and the internal electrode may inhibit sintering of a metal by adding a ceramic inhibitor to a metal paste for an internal electrode. The ceramic inhibitor is used as a sintering delaying material. When a nickel powder is used for a metal powder for the internal electrode, the ceramic inhibitor may minimize a shrinkage difference with a dielectric material by maximally delaying a sintering shrinkage temperature point of nickel (Ni) at which sintering starts, that is, by initiating the sintering shrinkage at a relatively high temperature compared to a relatively low temperature of about 400 to 500° C.
The ceramic inhibitor serves to delay sintering of Ni that is the internal electrode during a sintering process of the MLCC, and comes out of to a dielectric layer when sintering of Ni is completed and thereby affects an electrical characteristic of the dielectric material. Accordingly, a powder similar to a dielectric composition is used as an inhibitor. Also, when a size of the ceramic inhibitor is greater than a size of metal powder, a filling rate decreases, sintering shrinkage increases, sintering of the metal powder is not effectively controlled, and thus, a sintering starting temperature decreases. Accordingly, the ceramic inhibitor having a particle size less than the metal powder is generally used as a sintering delaying material.
Japanese Publication Patent No. 2000-269073 (published date: Sep. 29, 2000.) discloses a multilayer ceramic condenser and a manufacturing method thereof that may manufacture a metal paste for an internal electrode by adding, to a metal powder, ceramic inhibitor BaTiO3 and one of La and Cr that are rare-earth elements. Japanese Publication Patent No. 2000-269073 may increase content of the ceramic inhibitor BaTiO3 by adding the rare-earth element La or Cr to the metal paste for the internal electrode. Accordingly, continuity of the internal electrode is secured and capacitance of the MLCC increases.
Even though the method of manufacturing the metal paste for the internal electrode of the MLCC according to the related art may increase content of ceramic inhibitor through addition of a rare-earth element, the rare-earth element is diffused to a dielectric sheet to thereby be against a dielectric component. Accordingly, an electrical characteristic of the MLCC may vary and the average particle size of a ceramic inhibitor powder may significantly increase. Accordingly, it may be difficult to form the internal electrode to be thin and it is also difficult to achieve ultra high capacitance of the MLCC.